The present invention has particular utility in connection with the testing of single and multi-cylinder spark ignited engine ignition systems and is described herein as applied to such use. In evaluating an engine ignition system, certain visible operating characteristics of the spark arc across the electrodes of the spark plug are indicative of ignition system performance. Particularly, abnormal color, low intensity, or non-uniform firing frequency of the spark arc are characteristic of unacceptable system function.
Therefore, in diagnosing and troubleshooting an ignition system, it is best to test the ignition system from the position of the spark plug by observing the visual attributes of the spark arc. Moreover, it is desirable to evaluate the system under simulated operating conditions wherein the ignition system is functioning under a selectively variable load (e.g., subjecting the spark gap to varying ambient pressures).
A known instrument for testing an ignition system in a single or multi-cylinder engine is shown, for example, by U.S. Pat. No. 4,570,124. The instrument of this patent uses a commercial spark plug as the spark arc generation means. The spark plug is carried by a housing and the spark gap in the plug is positioned in a transparent chamber that can be pressurized. A pressure gage is mounted to the housing at an end opposite the spark plug in communication with the chamber. A manually operated air pump with a reciprocating pumping sleeve between the pressure gage and the spark plug pressurizes the chamber to subject the spark gap to various pressures. The instrument is connectable in circuit with an ignition voltage source of an engine. After such connection, the pumping sleeve is then reciprocated to pressurize the chamber to a desired level. The engine is then "turned over" and the characteristics of the spark arc across the spark plug's electrodes are observed.
In the past, the use and accommodation of a spark plug within the housing, and the complex pumping mechanism required to pressurize the chamber made the instrument somewhat expensive to manufacture and therefore sometimes not economically attractive to non-professionals who perform their own engine maintenance. Additionally, because the pumping sleeve was positioned between the spark plug and the pressure gauge, the stroke of the pumping sleeve was short. Therefore, several reciprocations of the pumping sleeve were required to attain maximum system pressure. Check valves and multiple seal arrangements were also needed to maintain the system pressure at a desired level.
It is important that an ignition system test instrument of the type in question be simple and straightforward to use. Additionally, such an instrument should be capable of economical manufacture.
Accordingly, the general object of the present invention is to provide an ignition system test instrument for testing both single and multi-cylinder engines that is easy to use and can be manufactured at relatively low cost.
A further object of the present invention is to provide an ignition system test instrument wherein the system can be pressurized to a desired pressure level without having to manually cycle the pump a multiple number of times.
It is yet a further object of the present invention to provide an ignition system test instrument of the foregoing character wherein the desired system pressure can be established and maintained without the use of check valves or multiple seal arrangements.